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OI-codes/S2OJ/1547/1547.cpp

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#include <iostream>
#include <algorithm>
#include <cmath>
#include <functional>
#include <limits>
#include <vector>
using std::cin;
using std::cout;
const char endl = '\n';
const int N = 5e5 + 5;
const long long INF = 1e18;
int n, m, w[N];
long long f[N][2];
std::vector<int> g[N];
void dfs(int u, int fa) {
int k = g[u].size() / 2 + 1;
long long res = 0;
std::vector<long long> a;
for (int v : g[u]) {
if (v == fa) continue;
dfs(v, u);
if (w[v] <= w[u]) {
a.emplace_back(std::max(f[v][0] + w[v], f[v][1] + w[u]) - f[v][1] - m);
res += f[v][1] + m;
} else {
a.emplace_back(f[v][0] + w[u] - std::max(f[v][0] + w[v], f[v][1] + m));
res += std::max(f[v][0] + w[v], f[v][1] + m);
}
}
std::sort(a.begin(), a.end(), std::greater<>());
if (k - 1 > a.size()) {
f[u][0] = -INF;
} else {
long long sum = res;
for (int i = 0; i < k - 1; i++) sum += a[i];
for (int i = k - 1; i < a.size(); i++) sum += std::max(0ll, a[i]);
f[u][0] = sum;
}
if (k > a.size()) {
f[u][1] = -INF;
} else {
long long sum = res;
for (int i = 0; i < k; i++) sum += a[i];
for (int i = k; i < a.size(); i++) sum += std::max(0ll, a[i]);
f[u][1] = sum;
}
}
int main() {
std::ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> m;
for (int i = 1; i <= n; i++) {
cin >> w[i];
}
for (int i = 1, u, v; i < n; i++) {
cin >> u >> v;
g[u].emplace_back(v);
g[v].emplace_back(u);
}
dfs(1, 1);
cout << f[1][1] << endl;
return 0;
}